1. Field of the Invention
The present invention is directed to respiration monitors and, in particular, to automatic x-ray machine triggering systems for use on uncooperative subjects.
2. Description of the Prior Art
In the medical field, it is frequently desirable to monitor a given subject's respiration. For example, x-ray pictures for study of the lungs should be taken at points of maximum inhalation when the lungs are fully inflated. Similarly, x-ray pictures for examination of the area surrounding the lungs should be taken at points of maximum exhalation, when the lungs are fully deflated. Such instants of maximum inhalation or exhalation shall hereinafter be collectively termed "instants of respiration extrema." In practice, the x-ray machine operator instructs the subject to inhale or exhale and maintain that condition while the x-ray picture is taken. A problem, however, rises when a chest x-ray is taken of an uncooperative subject, such as an unconscious adult, an infant or an animal. U.S. Pat. No. 3,524,058 issued Aug. 11, 1970 to Robertson et al. is directed to a respiration monitor for use in an x-ray triggering system whereby instants of maximum inhalation and exhalation are detected to automatically trigger the x-ray machine. Such respiration monitor, however, requires a physical connection to the subject's body. Specifically, electrodes are connected to the subject to direct an electric current through a particular portion of the subject's body, and the modulation of the current by the subject's body is monitored to detect points of maximum inhalation or exhalation. Other respiration monitors utilize masks and nasal insertions. Such prior art systems, in requiring such physical connections to the subject, have disadvantages that render the use of such systems undesirable.